The pupil detection has been recognized as an effective means for estimating the intention of an examinee by capturing a characteristic point of a human face, and for acquiring information about point at and from which an examinee's is looking. Many kinds of studies and inventions have been conducted in regard to the pupil detection itself and the application thereof (Patent documents 1-4 and Non-patent document 1). The pupil is excellent as a detection object because the pupil itself is small, and not only basically viewed as a circle or an ellipse from any directions, but hard to be concealed behind the eyelid, differently from an iris. By the use thereof, it has been proposed to make a pupil moving amount correspond to cursor movement on a personal computer screen, and also, the cursor can be moved relative to the movement of the head.
Further, using the pupil detection technique, there are requirements for detecting eyes, sleepiness and inattentive driving of a passenger car driver and a truck driver. In such cases, it has been desired to stably enable the pupil detection even under a bad environment such that human faces are exposed to direct sunlight.    Patent document 1: Japanese Patent Application No. 2004-73998    Patent document 2: Japanese Patent Application Laid-open No. 2004-261598    Patent document 3: Japanese Patent Publication No. 2002-513176    Patent document 4: Japanese Patent Application Laid-open No. Hei-11-56782    Non-patent document 1: “Pupil detection and tracking using multiple light sources”, C. H. Morimoto, D. Koons, A. Amir, and M. Flickner, Image and Vision Computing 18 (2000), 331-335